package qj.tool.converter;

/**
 * Check commons codec
 */
public class Base64Converter {

    private static final char [ ] chrAlphabet = {
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',   //  0 to  7
            'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',   //  8 to 15
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',   // 16 to 23
            'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',   // 24 to 31
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',   // 32 to 39
            'o', 'p', 'q', 'r', 's', 't', 'u', 'v',   // 40 to 47
            'w', 'x', 'y', 'z', '0', '1', '2', '3',   // 48 to 55
            '4', '5', '6', '7', '8', '9', '+', '/'}; // 56 to 63

    /**
     *
     * @param s
     * @return encoded String
     */
    public static String encode(String s) {
        return encode(s.getBytes());
    }

    /**
     *
     * @param octetString
     * @return encoded String
     */
    public static String encode(byte [ ]  octetString) {
        int bits24;
        int bits6;

        char [ ]  out
                = new char [ ((octetString.length - 1) / 3 + 1) * 4 ];

        int outIndex = 0;
        int i = 0;

        while ((i + 3) <= octetString.length) {
            // store the octets
            bits24 = (octetString[i++] & 0xFF) << 16;
            bits24 |= (octetString[i++] & 0xFF) << 8;
            bits24 |= (octetString[i++] & 0xFF);

            bits6 = (bits24 & 0x00FC0000) >> 18;
            out[outIndex++] = chrAlphabet[bits6];
            bits6 = (bits24 & 0x0003F000) >> 12;
            out[outIndex++] = chrAlphabet[bits6];
            bits6 = (bits24 & 0x00000FC0) >> 6;
            out[outIndex++] = chrAlphabet[bits6];
            bits6 = (bits24 & 0x0000003F);
            out[outIndex++] = chrAlphabet[bits6];
        }

        if (octetString.length - i == 2) {
            // store the octets
            bits24 = (octetString[i] & 0xFF) << 16;
            bits24 |= (octetString[i + 1] & 0xFF) << 8;

            bits6 = (bits24 & 0x00FC0000) >> 18;
            out[outIndex++] = chrAlphabet[bits6];
            bits6 = (bits24 & 0x0003F000) >> 12;
            out[outIndex++] = chrAlphabet[bits6];
            bits6 = (bits24 & 0x00000FC0) >> 6;
            out[outIndex++] = chrAlphabet[bits6];

            // padding
            out[outIndex++] = '=';
        } else if (octetString.length - i == 1) {
            // store the octets
            bits24 = (octetString[i] & 0xFF) << 16;

            bits6 = (bits24 & 0x00FC0000) >> 18;
            out[outIndex++] = chrAlphabet[bits6];
            bits6 = (bits24 & 0x0003F000) >> 12;
            out[outIndex++] = chrAlphabet[bits6];

            // padding
            out[outIndex++] = '=';
            out[outIndex++] = '=';
        }

        return new String(out);
    }

}
